We report a basin-hopping Monte Carlo investigation within the embedded-
atom method of the structural and energetic properties of bimetallic
ZrCu, ZrAl, and CuAl nanoclusters with 55 and 561 atoms. We found that
unary Zr-55, Zr-561, Cu-55, Cu-561, Al-55, and Al-561 systems adopt the
well known compact icosahedron (ICO) structure. The excess energy is
negative for all systems and compositions, which indicates an energetic
preference for the mixing of both chemical species. The ICO structure is
preserved if a few atoms of the host system are replaced by different
species, however, the composition limit in which the ICO structure is
preserved depends on both the host and new chemical species. Using
several structural analyses, three classes of structures, namely ideal
ICO, nearly ICO, and distorted ICO structures, were identified. As the
amounts of both chemical species change towards a more balanced
composition, configurations far from the ICO structure arise and the
dominant structures are nearly spherical, which indicates a strong
minimization of the surface energy by decreasing the number of atoms
with lower coordination on the surface. The average bond lengths follow
Vegard's law almost exactly for ZrCu and ZrAl, however, this is not the
case for CuAl. Furthermore, the radial distribution allowed us to
identify the presence of an onion-like behavior in the surface of the
561-atom CuAl nanocluster with the Al atoms located in the outermost
surface shell, which can be explained by the lower surface energies of
the Al surfaces compared with the Cu surfaces. In ZrCu and ZrAl the
radial distribution indicates a nearly homogeneous distribution for the
chemical species, however, with a slightly higher concentration of Al
atoms on the ZrAl surface, which can also be explained by the lower
surface energy.